1. Field of the Invention
The present invention is directed to flow check valves and, more particularly, to such flow check valves that are reversible thereby permitting fluid flow in either desired direction.
2. Setting of the Invention
The use of check valves, which include a clapper mechanism for stopping the flow of fluid in one direction but permitting it in another direction, is well known. Conventional check valves are normally designed to be unidirectional, that is, permit flow in one direction and block flow in the other direction, and there is no mechanism of reversing this condition without removing pressure from the line in which it is installed, draining, disassembling and removing the clapper or the valve from its installation and reversing its orientation, or constructing costly by-passes around the check valve.
Others have developed check valves in which the check action of the clapper mechanism can be reversed, that is, in one position the valve permits flow in a first direction but prohibits flow in a second direction, and in which the internal orientation of the valve can be reversed so that the valve then permits flow in the second direction but prevents flow in the first direction. Reversible check valves are disclosed in the following U.S. Pat. Nos.: 3,851,665; 3,474,818; 3,363,650; 1,175,328; 2,151,098; and 3,344,808 and in copending U.S. patent application Ser. No. 390,279, filed 8/7/89.
Conventional reversible check valves require complicated sealing mechanisms and expensive machining and finishing of a plug and receiver for same in which the clapper is secured. Further, these devices must have a relatively large body-to-flow area ratio due to their basic arrangements. The possibility of valve failure due to seal failure increases due to the greater number of seals and/or sealing or machined surfaces in these devices. Further, the sealing surfaces of each of these devices experience wear and suffer abrasion when rotated or reversed. Due to their designs each reversal will deteriorate these valves+ sealing abilities, and therefore the life of these valves is shortened with each such reversal.
These valves do not permit the clapper to be retracted to a stored position to permit essentially unobstructed fluid flow therethrough. Some conventional check valves are provided with an extension of the clapper pivot shaft that extends externally of the valve body on which a wrench may be used to open the clapper. Although adequate for some purposes, the seals required around this extension of the shaft deteriorate with every movement of the clapper, and the danger is always present that the clapper may accidentally close on the seat should there be a mechanical failure within the valve, or a pressure surge, with resultant catastrophic consequences.
As there are numerous pipelines, injection and processing facilities that require reverse flow capability, there is a need for a reversible flow check valve that eliminates the above described problems associated with wear on valve seals and seats with rotational movement. There is a need for a reversible flow check valve that can have its clapper retracted when necessary for reverse flow, or when pipeline pigs or other equipment is passed therethrough, with the hazard of accidental closing eliminated.
Another problem associated with the opening and/or retraction of clappers in check valves is that of high pressure downstream of the clapper and low pressure upstream, as can occur when pumps or compressors stop. In high pressure applications, the force exerted on the clapper in the direction toward the clapper's seat can be relatively tremendous, and any attempt to open or retract the clapper is futile. Although bypasses around valves to reduce pressure differentials are known in the industry, there is a need for a device to reduce pressure differentials that is integral with the clapper of a check valve so that its function can be accomplished using the same device used to open the clapper, without the need for external piping, controls, or devices.